The present invention relates to a system for controlling an automatic vehicle transmission apparatus including a gear transmission and a clutch, both of which are electronically controlled.
In the prior art an automatic transmission system for vehicles including a gear transmission and a clutch which are electronically controlled by an electronic control unit is well known. In the conventional automatic transmission system of such type, when the ignition switch is turned to its OFF position, the power supply for the electronic control unit is maintained even after fuel combustion in the engine has stopped whereas operations for the gear transmission and the clutch are ceased.
Accordingly, the following disadvantages will occur when a power steering system and/or a power braking system powered by the associated internal combustion engine is employed in the vehicle.
If the gear transmission is shifted to its neutral position or the clutch is in a disconnected condition at the time the ignition switch is turned to the OFF position to stop the fuel combustion in the engine, since the rotational torque of the axle caused by vehicle running cannot be transmitted to the output shaft of engine, the rotational speed of the engine immediately becomes zero. This immediately makes the power steering system and the power braking system inoperable because the engine rotation stops even though the vehicle continues to run. As a result, it is difficult to maintain the power steering system and the power braking system in an adequately safe operating condition until the vehicle stops. This is a dangerous state of vehicle operation.